Not all composts / manures are safe / beneficial

As a descendant of the Rodale tradition of compost = garden gold, it can be hard for me to learn that not all compost and not all manures are good. Some can even be toxic and kill your garden.

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National Gardening AssociationClopyralid (herbicide), used in lawn care, has shown up as a contaminant in composting facilities from Pennsylvania to Washington.Clopyralid-contaminated compost can be toxic to sunflowers, peas, beans, tomatoes, and potatoes.... clopyralid doesn't break down under normal composting processes, and it can be a hazard to these plants even at low concentrations.

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grist.orgCalifornia regulators traced residues of dichlorophenyl-dichloroethylene, a breakdown product of DDT, and bifenthrin, an ant killer, to compost in pots of organic wheatgrass ...DDT was banned for most uses in the early ’70s and bifenthrin is classified as a possible human carcinogen and is highly toxic to fish. The NOP initially proposed setting a strict upper limit for bifenthrin levels in compost but abandoned the idea when wider tests revealed that many brands of commercial compost wouldn’t pass. Regulators ultimately decided to allow any level of contamination in compost so long as “residual pesticide levels do not contribute to the contamination of crops, soil, or water.”

Terrible story from the UK. Dow produced herbicide that was used for crops that were fed to cattle. The cattle manure was sold to gardeners. The herbicide damaged garden vegetables and ruined the soil.

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MotherEarthNews.comclopyralid and its close cousin, aminopyralid, easily persist, sometimes for YEARS!, in hay, manure and compost....used in food gardens, tomatoes, beans and other sensitive crops develop curled foliage that looks like a disease, if they grow at all. alsoDow herbicides in composts.

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Ohio State University Extension. "as little as 2 parts per million (ppm) of 2,4-D (Weed-B-Gone) or 50 parts per billion of Clopyralid significantly reduce the growth of sensitive plants like tomato" although they report most pesticides degrade rapidly. also clopyralid is very persistent in composts and manures and is largely unaffected by the composting process. Most plants are not damaged by clopyralid, even at rates used on lawns and agricultural crops. However, plants in the bean family (Leguminosae), the potato/tomato family (Solonaceae), and the sunflower family (Compositae) are very sensitive to this herbicide. It can stunt tomato, clover, lettuce, pea, lentil, sunflower, pepper, and bean plants at levels in compost as low as 10 parts per BILLION! Since the level of clopyralid on grass the day of application is 10,000 to 50,000 ppb, even a small amount of contaminated material entering a composting facility or directly applied to sensitive crops can cause major problems.

Looks like Clopyralid is banned, but as a home product may continue to show up in city yard-waste compost as chemical-using homeowners use up their supplies. Then, of course, there is always the next product on the market, and no one will know until there is another disaster.

None of this is meant to scare anyone off from using commercial composts or manures. I've been using local yard debris compost to enrich my garden for over a decade. Lately I've been mixing it into my new raised beds, adding about 25% to the otherwise poor topsoil. It makes a big difference in fertility, drainage, workability, soil texture, and plant growth. I've been to the composting center - they have big mountains of compost. I hope any contaminants are well diluted and most are degraded. Without the compost, my garden would be much less productive and fertile. Still, whenever possible I'm using my own leaves, grass, chicken manure, etc. I do think it's important to know what we are doing, and be aware there is potential harm in something we think is universally good.

Replies to This Discussion

Yes, we had a situation several years ago where our garden recycle was made available for the public and it contained some chemical weed killer on grass and caused failures of garden vegetables and fruit. I don't know if the city checks for such chemicals now. I have had no problem, but I do not have one blade of grass growing in my yard, and I use no commercial chemicals. I also use beneficial insects and that takes care of most pests. Diseases, such as fungi, require specific management, like open up the density so light and air can circulate around plants. I cut away leaves and branches with fungus and sterilize my pruners with alcohol that I keep in the garden. I wash my gloves that are exposed to fungus. I find that going all natural, like using pyrethrum, I don't the as many problems as gardeners who spray the whole property.

Sentient, you wrote, "None of this is meant to scare anyone off from using commercial composts or manures." People need to know that commercial products may not be as safe as a gardener needs, and with a little observing and questioning and talking over fences one can cut back on unnecessary problems. It is one thing to have a problem causes by something I did or did not do, but quite another when chemicals are used improperly and indiscriminately.

You are right, it's a problem to suffer from the wrong actions of others. Herbicide drift from neighbors, and their pesticide drift, fertilizer drift, farmers getting the genetically engineered pollen from neighboring farms. And thinking we are buying a healthy organic product, when it is really poison.

From Mother Earth News, looks like the situation is as bad as ever. Some compost products, including comercial compost and composted manures, are contaminated with persistent, powerful herbicides. Digestion and composting does not remove these toxic substances.

It's got me a bit concerned. I bought several truckloads of yard waste compost to improve my vegetable beds. I'm going to do as much as possible myself, but this year needed more than I can make.

James, do you know what herbicides your local ranchers use? I'm curious. The herbicides may also come in the form of feeds the ranchers buy, unless they grow their own and are not using herbicides on their farms. Not that I know.